The invention relates to a rod drive control system for power nuclear reactors and, more particularly, to the rod drive control system with stepping motors.
The reactor power and power distribution of nuclear power reactors are controlled or adjusted by means of driving control rods of approximately 200, which are provided within the nuclear reactor, to and from the nuclear reactor core. By convention, the positioning of the control rod is carried out by using a magnetic jack or a hydraulic drive mechanism. In a high-power run of the reactor, it is desirable that the unitary stepwise motion of the control rod for its positioning purpose is as small as possible. Conversion of a rotary motion of a drive motor into a rectilinear motion by means of a screw mechanism has been used for this fine positioning of the control rod. This fine positioning method has been employed particularly in the numerical control machine tool. The positioning control of the control rod is very important, from a safety point of view. The following cases, for example, should be avoided for ensuring the safety of the nuclear power plant. The first case is that, even when no operation signal is applied to a control rod, the control rod automatically moves. The second is that the control rod moves in the opposite direction to that directed by a command signal.
Such cases arise from faults of components, introduction of external noise into the control unit, or the like. The conventional numerical control system is compelled to take a compromise countermeasure for the problem of minimizing fault occurence and system cost rise. The compromise countermeasure taken hinders a satisfactory solution of the problem.